Paper mills have for many years made extensive use, for the cleaning of paper making stock, of pressure screening apparatus embodying a cylindrical perforated screening member defining supply and accepts chambers on the opposite sides thereof in a closed housing, and including a rotor member which operates in one of the chambers to keep the screening perforations open and free from solid material tending to cling to the screening surface. Commonly, the stock or furnish is delivered to the supply chamber adjacent one end of the screening cylinder, and the material rejected oy the screening cylinder is collected and discharged from the opposite end of the supply chamber.
The assignee of this invention has manufactured many such screens in accordance with a series of U.S. patents, commencing with Staege U.S. Pat. No. 2,347,716, and followed by Martindale U.S. Pat. No. 2,835,173, Seifert U.S. Pat. Nos. 3,849,302 and 4,105,543, Seifert-Chupka U.S. Pat. No. 3,970,548 and Chupka-Seifert U.S. Pat. Nos. 4,155,841 and 4,383,918. These patents demonstrate substantial detailed variation in screens of the above type, especially in the size, configuration and spacing of the perforations in the screening cylinder. Less consideration has been given to improving the construction and operation of the rotor, however, except for Seifert-Chupka '548 wherein the rotor is of special construction for enabling the screen to handle dirty stock, and particularly stock having multiple stringy contaminants.